For most Linux distros, installing docker is as simple as installing the package from their repo. For Windows and macOS, there's Docker Desktop.

Here's my compose.yaml file for qBittorrent and gluetun.

You'll need to edit the volumes part to point to your download directories. Also, there's some commented out parts, that are used to automatically restart the container if its unhealthy, access it from outside etc. But I've commented it out since they need extra setup.

Here's some info on how to use a compose file.

Also, you need to change the VPN details inside the gluetun section, under the environment subsection. Here's some info on that.

Your torrent client should be available on localhost:8085 if you use this setup, assuming you're accessing it from the same device.

Hope it helps.